From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from atl4mhob05.myregisteredsite.com ([209.17.115.43]:43741 "EHLO atl4mhob05.myregisteredsite.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750732Ab3EUCRe (ORCPT ); Mon, 20 May 2013 22:17:34 -0400 Received: from mailpod1.hostingplatform.com ([10.30.71.115]) by atl4mhob05.myregisteredsite.com (8.14.4/8.14.4) with ESMTP id r4L2HWFY004939 for ; Mon, 20 May 2013 22:17:32 -0400 Message-ID: <519AD943.6060303@chinilu.com> Date: Mon, 20 May 2013 19:17:39 -0700 From: George Mitchell Reply-To: george@chinilu.com MIME-Version: 1.0 To: Duncan <1i5t5.duncan@cox.net> CC: linux-btrfs@vger.kernel.org Subject: Re: Virtual Device Support References: <518CFE3A.3080900@chinilu.com> <20130519171510.54897415@natsu> <262CC063-0DB4-45BD-A776-9FD1E8650E7C@colorremedies.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Duncan, The problem affects btrfs volumes that span multiple drive. If you are using btrfs on a single drive that works just fine. But in a multidrive situation, sometimes it works (when umount guesses the right device name) and sometimes it fails (when umount guesses the wrong device name). Have fun! - George On 05/20/2013 06:08 PM, Duncan wrote: > Chris Murphy posted on Sun, 19 May 2013 12:18:19 -0600 as excerpted: > > >> On May 19, 2013, at 5:15 AM, Roman Mamedov wrote: >> >>> From a user perspective btrfs subvolumes have a lot in common with just >>> regular directories aka folders, and nothing in common with >>> (block)devices. >>> "Describing them with virtual devices" does not seem to make a whole >>> lot of sense. >> It's not possible to mount regular directories with other file systems. > Actually, it /is/ possible, using bind-mounts, etc. These even work at > the individual file level, and I use a few that way here, for mounting > usable device files over an otherwise nodev mounted filesystem (used for > a named/bind chroot, bind-mounted and then remounted nodev,noexec, etc.). > > But yes, bind-mounts are an exception to the general rule. However, > they're an exception that does make your above claim questionable, at > least. btrfs subvolumes are another such exception. > >> In some ways the btrfs subvolume behaves like a folder. In other ways it >> acts like a device. If you stat the mount point for btrfs subvolumes, >> you get a unique device ID for each. > Agreed. > >> It seems inconsistent that mount and unmount allows a /dev/ designation, >> but only mount honors label and UUID. > Yes. I had tested btrfs a year ago and decided to wait so haven't been > active here for 8 months or so, but am now getting back into btrfs as my > requirements are different now, and as I'm reading the list, I've seen > this frustrating inconsistency complained about more than once. I'm > about to setup a new btrfs system here once again, so don't yet know if > it'll affect me personally, but given that I routinely use labels in > fstab, it certainly could, depending on how the umounts are handled. But > at least I have a heads-up on the issue and can thus work around it > should I need to. >